Golf balls having a low modulus HNP layer and a high modulus HNP layer

ABSTRACT

The present invention is directed to golf balls having a layer formed from a low modulus HNP composition and a layer formed from a high modulus HNP composition. Golf balls of the present invention have at least three layers, including an inner core layer, an outer core layer, a cover, and optionally an intermediate core layer. The present invention is not limited by which golf ball layers are formed from an HNP composition, so long as at least one layer is formed from a low modulus HNP composition and at least one layer is formed from a high modulus HNP composition. Low modulus HNP compositions of the present invention comprise a highly neutralized acid copolymer having a modulus of from 1,000 psi to 50,000 psi. High modulus HNP compositions of the present invention comprise a highly neutralized acid copolymer having a modulus of from 25,000 psi to 150,000 psi.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 10/797,810, filed Mar. 10, 2004 now U.S. Pat. No. 6,988,962, and U.S. patent application Ser. No. 10/797,699, filed Mar. 10, 2004 now U.S. Pat. No. 6,981,926, the entire disclosures of which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to golf balls comprising a layer formed from a low modulus HNP composition and a layer formed from a high modulus HNP composition. The present invention is not limited by which layer is formed from the low modulus HNP composition and which layer is formed from the high modulus HNP composition, so long as both layers are present in the golf ball.

BACKGROUND OF THE INVENTION

Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.

Golf ball core and cover layers are typically constructed with polymer compositions including, for example, polybutadiene rubber, polyurethanes, polyamides, ionomers, and blends thereof. Ionomers, particularly ethylene-based ionomers, are a preferred group of polymers for golf ball layers because of their toughness, durability, and wide range of hardness values.

Golf ball compositions comprising highly neutralized acid polymers are known. For example, U.S. Patent Application Publication No. 2003/0130434, the entire disclosure of which is hereby incorporated herein by reference, discloses melt-processible, highly-neutralized ethylene acid copolymers and process for making them by incorporating an aliphatic, mono-functional organic acid in the acid copolymer and then neutralizing greater than 90% of all the acid groups present. The use of such compositions in various golf ball layers is disclosed. Also, U.S. Patent Application Publication No. 2005/0148725, the entire disclosure of which is hereby incorporated herein by reference, discloses a highly-resilient thermoplastic composition comprising (a) an acid copolymer, (b) a salt of a high molecular weight, monomeric organic acid; (c) a thermoplastic resin; (d) a cation source; and (e) optionally, a filler. The reference also discloses one-piece, two-piece, three-piece, and multi-layered golf balls comprising the highly-resilient thermoplastic composition.

While various uses for highly neutralized acid polymers in golf balls have been discovered, there is a need in the industry to broaden the applicability of highly neutralized acid polymers to particular golf ball constructions having desirable spin, feel, and COR properties. The present invention provides such golf ball constructions through the use of a layer formed from a low modulus HNP composition and a layer formed from a high modulus HNP composition.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a golf ball comprising an inner core layer, an outer core layer, and a cover. The inner core layer is formed from a low modulus HNP composition comprising a highly neutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer having a modulus of from 1,000 psi to 50,000 psi. The outer core layer is formed from a high modulus HNP composition comprising a highly neutralized ethylene/(meth)acrylic acid copolymer having a modulus of from 45,000 psi to 150,000 psi. The modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 10% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.

In another embodiment, the present invention is directed to a golf ball comprising an inner core layer, an outer core layer, and a cover. The inner core layer is formed from a high modulus HNP composition comprising a highly neutralized ethylene/(meth)acrylic acid copolymer having a modulus of from 25,000 psi to 150,000 psi. The outer core layer is formed from a low modulus HNP composition comprising a highly neutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer having a modulus of from 1,000 psi to 50,000 psi. The modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 10% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.

In another embodiment, the present invention is directed to a golf ball comprising an inner core layer, an outer core layer, an intermediate core layer disposed between the inner core layer and the outer core layer, and a cover. The inner core layer comprises a diene rubber composition, the intermediate core layer is formed from a low modulus HNP composition, and the outer core layer is formed from a high modulus HNP composition. The low modulus HNP composition comprises a highly neutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer having a modulus of from 1,000 psi to 50,000 psi. The high modulus HNP composition comprises a highly neutralized ethylene/(meth)acrylic acid copolymer having a modulus of from 45,000 psi to 150,000 psi. The modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 10% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.

In yet another embodiment, the present invention is directed to a golf ball comprising an inner core layer, an outer core layer, an intermediate core layer disposed between the inner core layer and the outer core layer, and a cover, wherein the inner core layer comprises a diene rubber composition, the intermediate core layer is formed from a high modulus HNP composition, and the outer core layer is formed from a low modulus HNP composition. The high modulus HNP composition comprises a highly neutralized ethylene/(meth)acrylic acid copolymer having a modulus of from 25,000 psi to 150,000 psi. The low modulus HNP composition comprises a highly neutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer having a modulus of from 1,000 psi to 50,000 psi. The modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 10% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.

DETAILED DESCRIPTION OF THE INVENTION

Golf balls of the present invention have at least two layers formed from highly neutralized acid polymer (“HNP”) compositions. More particularly, golf balls of the present invention have at least one layer formed from a low modulus HNP composition, and at least one layer formed from a high modulus HNP composition.

As used herein, “highly neutralized acid polymer” refers to an acid polymer after at least 80%, preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of the acid groups of the acid polymer are neutralized.

As used herein, “modulus” refers to flexural modulus as measured using a standard flex bar according to ASTM D790-B.

Low Modulus HNP Composition

Low modulus HNP compositions of the present invention comprise at least one low modulus HNP having a modulus within the range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 17,000 or 25,000 or 28,000 or 30,000 or 35,000 or 45,000 or 50,000 or 55,000 psi. In a preferred embodiment, the modulus of the low modulus HNP is at least 10% less, or at least 20% less, or at least 25% less, or at least 30% less, or at least 35% less, than the modulus of the high modulus HNP.

Low modulus HNPs of the present invention are salts of acid copolymers. It is understood that the low modulus HNP may be a blend of two or more low modulus HNPs. The acid copolymer of the low modulus HNP is an O/X/Y-type copolymer, wherein O is an α-olefin, X is a C₃–C₈ α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer. O is preferably ethylene. X is preferably selected from (meth) acrylic acid, ethacrylic acid, maleic acid, crotonic acid, fumaric acid, and itaconic acid. (Meth) acrylic acid is particularly preferred. As used herein, “(meth) acrylic acid” means methacrylic acid and/or acrylic acid. Likewise, “(meth) acrylate” means methacrylate and/or acrylate. Y is preferably an alkyl (meth) acrylate, wherein the alkyl groups have from 1 to 8 carbon atoms. Preferred O/X/Y-type copolymers are those wherein O is ethylene, X is (meth) acrylic acid, and Y is selected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate. Particularly preferred O/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butyl acrylate, ethylene/(meth) acrylic acid/methyl acrylate, and ethylene/(meth) acrylic acid/ethyl acrylate.

The acid copolymer of the low modulus HNP typically includes the α-olefin in an amount of at least 15 wt %, or at least 25 wt %, or at least 40 wt %, or at least 60 wt %, based on the total weight of the acid copolymer. The amount of C₃–C₈ α,β-ethylenically unsaturated carboxylic acid in the acid copolymer is typically within the range having a lower limit of 1 or 4 or 6 or 8 or 10 or 15 wt % and an upper limit of 20 or 35 or 40 wt %, based on the total weight of the acid copolymer. The amount of softening monomer in the acid copolymer is typically within the range having a lower limit of 1 or 3 or 5 or 11 or 15 or 20 wt % and an upper limit of 23 or 25 or 30 or 35 or 50 wt %, based on the total weight of the acid copolymer.

Particularly suitable acid copolymers of the low modulus HNP include very low modulus ionomer- (“VLMI-”) type ethylene-acid polymers, such as Surlyn® 6320, Surlyn® 8120, Surlyn® 8320, and Surlyn® 9320. Surlyn® ionomers are commercially available from E.I. du Pont de Nemours and Company. Also suitable are DuPont® HPF 1000 and DuPont® HPF 2000, ionomeric materials commercially available from E.I. du Pont de Nemours and Company.

Additional suitable acid copolymers of the low modulus HNP are disclosed, for example, in U.S. Patent Application Publication Nos. 2005/0148725, 2005/0020741, 2004/0220343, and 2003/0130434, and U.S. Pat. Nos. 5,691,418, 6,562,906, 6,653,382, 6,777,472, 6,762,246, and 6,815,480, the entire disclosures of which are hereby incorporated herein by reference.

In a preferred embodiment, the low modulus HNP is formed by reacting an acid copolymer, which is optionally partially neutralized, with a sufficient amount of cation source, in the presence of a high molecular weight organic acid or salt thereof, such that at least 80%, preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of all acid groups present are neutralized. The acid copolymer can be reacted with the high molecular weight organic acid or salt thereof and the cation source simultaneously, or the acid copolymer can be reacted with the high molecular weight organic acid prior to the addition of the cation source.

Suitable high molecular weight organic acids are aliphatic organic acids, aromatic organic acids, saturated monofunctional organic acids, unsaturated monofunctional organic acids, multi-unsaturated monofunctional organic acids, and dimerized derivatives thereof. Particular examples of suitable organic acids include, but are not limited to, caproic acid, caprylic acid, capric acid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylacetic acid, naphthalenoic acid, dimerized derivatives thereof, and combinations thereof. Salts of high molecular weight organic acids comprise the salts, particularly the barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium, stontium, titanium, tungsten, magnesium, and calcium salts, of aliphatic organic acids, aromatic organic acids, saturated monofunctional organic acids, unsaturated monofunctional organic acids, multi-unsaturated monofunctional organic acids, dimerized derivatives thereof, and combinations thereof. Suitable organic acids and salts thereof are more fully described, for example, in U.S. Pat. No. 6,756,436, the entire disclosure of which is hereby incorporated herein by reference.

Suitable cation sources include metal ions and compounds of alkali metals, alkaline earth metals, and transition metals; metal ions and compounds of rare earth elements; silicone, silane, and silicate derivatives and complex ligands; and combinations thereof. Preferred cation sources are metal ions and compounds of magnesium, sodium, potassium, cesium, calcium, barium, manganese, copper, zinc, tin, lithium, and rare earth metals. The acid copolymer may be at least partially neutralized prior to contacting the acid copolymer with the cation source to form the low modulus HNP. Methods of preparing ionomers are well known, and are disclosed, for example, in U.S. Pat. No. 3,264,272, the entire disclosure of which is hereby incorporated herein by reference. The acid copolymer can be a direct copolymer wherein the polymer is polymerized by adding all monomers simultaneously, as disclosed, for example, in U.S. Pat. No. 4,351,931, the entire disclosure of which is hereby incorporated herein by reference. Alternatively, the acid copolymer can be a graft copolymer wherein a monomer is grafted onto an existing polymer, as disclosed, for example, in U.S. Patent Application Publication No. 2002/0013413, the entire disclosure of which is hereby incorporated herein by reference.

Low modulus HNP compositions of the present invention optionally contain one or more melt flow modifiers. The amount of melt flow modifier in the composition is readily determined such that the melt flow index of the composition is at least 0.1 g/10 min, preferably from 0.5 g/10 min to 10.0 g/10 min, and more preferably from 1.0 g/10 min to 6.0 g/10 min, as measured using ASTM D-1238, condition E, at 190° C., using a 2160 gram weight.

Suitable melt flow modifiers include, but are not limited to, high molecular weight organic acids and salts thereof, polyamides, polyesters, polyacrylates, polyurethanes, polyethers, polyureas, polyhydric alcohols, and combinations thereof. Suitable organic acids are aliphatic organic acids, aromatic organic acids, saturated mono-functional organic acids, unsaturated monofunctional organic acids, multi-unsaturated mono-functional organic acids, and dimerized derivatives thereof. Particular examples of suitable organic acids include, but are not limited to, caproic acid, caprylic acid, capric acid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylacetic acid, naphthalenoic acid, dimerized derivatives thereof. Suitable organic acids are more fully described, for example, in U.S. Pat. No. 6,756,436, the entire disclosure of which is hereby incorporated herein by reference.

Additional melt flow modifiers suitable for use in compositions of the present invention, include the non-fatty acid melt flow modifiers described in copending U.S. patent application Ser. Nos. 11/216,725 and 11/216,726, the entire disclosures of which are hereby incorporated herein by reference.

Low modulus HNP compositions of the present invention optionally include additive(s) and/or filler(s) in an amount of 50 wt % or less, or 30 wt % or less, or 15 wt % or less, based on the total weight of the low modulus HNP composition. Suitable additives and fillers include, but are not limited to, chemical blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, UV absorbers, light stabilizers, defoaming agents, processing aids, mica, talc, nano-fillers, antioxidants, stabilizers, softening agents, fragrance components, plasticizers, impact modifiers, TiO₂, acid copolymer wax, surfactants, and fillers, such as zinc oxide, tin oxide, barium sulfate, zinc sulfate, calcium oxide, calcium carbonate, zinc carbonate, barium carbonate, clay, tungsten, tungsten carbide, silica, lead silicate, regrind (recycled material), and mixtures thereof. Suitable additives are more fully described in, for example, U.S. Patent Application Publication No. 2003/0225197, the entire disclosure of which is hereby incorporated herein by reference.

Low modulus HNP compositions of the present invention optionally contain a high modulus HNP.

Low modulus HNP compositions of the present invention preferably have a hardness within the range having a lower limit of 40 or 50 or 55 Shore C and an upper limit of 70 or 80 or 87 Shore C.

In a particular embodiment, the low modulus HNP composition has a moisture vapor transmission rate of 8 g-mil/100 in²/day or less (i.e., 3.2 g-mm/m²·day or less), or 5 g-mil/100 in²/day or less (i.e., 2.0 g-mm/m²·day or less), or 3 g-mil/100 in²/day or less (i.e., 1.2 2·day or less), or 2 g-mil/100 in²/day or less (i.e., 0.8 g-mm/m²·day or less), or 1 g-mil/100 in²/day or less (i.e., 0.4 g-mm/m²·day or less), or less than 1 g-mil/100 in²/day (i.e., less than 0.4 g-mm/m²·day). As used herein, moisture vapor transmission rate (“MVTR”) is given in g-mil/100 in²/day, and is measured at 20° C. and according to ASTM F1249-99. In a preferred aspect of this embodiment, the low modulus HNP composition comprises a low modulus HNP prepared using a cation source which is less hydrophilic than conventional magnesium-based cation sources. Suitable moisture resistant HNP compositions are disclosed, for example, in copending U.S. patent application Ser. No. 11/270,066 and U.S. Patent Application Publication No. 2005/0267240, the entire disclosures of which are hereby incorporated herein by reference.

Low modulus HNP compositions of the present invention are not limited by any particular method or any particular equipment for making the compositions. In a preferred embodiment, the composition is prepared by the following process. The acid polymer(s), preferably a VLMI-type ethylene-acid terpolymer, high molecular weight organic acid(s) or salt(s) thereof, and optionally additive(s)/filler(s) are simultaneously or individually fed into a melt extruder, such as a single or twin screw extruder. A suitable amount of cation source is simultaneously or subsequently added such that at least 80%, preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of all acid groups present are neutralized. The acid polymer may be at least partially neutralized prior to the above process. The components are intensively mixed prior to being extruded as a strand from the die-head.

Low modulus HNP compositions of the present invention may be blended with one or more additional polymers, such as thermoplastic polymers and elastomers. Examples of thermoplastic polymers suitable for blending include, but are not limited to, bimodal ionomers (e.g., as disclosed in U.S. Patent Application Publication No. 2004/0220343 and U.S. Pat. Nos. 6,562,906 and 6,762,246, the entire disclosures of which are hereby incorporated herein by reference), ionomers modified with rosins (e.g., as disclosed in U.S. Patent Application Publication No. 2005/0020741, the entire disclosure of which is hereby incorporated by reference), soft and resilient ethylene copolymers (e.g., as disclosed U.S. Patent Application Publication No. 2003/0114565, the entire disclosure of which is hereby incorporated herein by reference) polyolefins, polyamides, polyesters, polyethers, polycarbonates, polysulfones, polyacetals, polylactones, acrylonitrile-butadiene-styrene resins, polyphenylene oxide, polyphenylene sulfide, styrene-acrylonitrile resins, styrene maleic anhydride, polyimides, aromatic polyketones, ionomers and ionomeric precursors, acid copolymers, conventional HNPs, polyurethanes, grafted and non-grafted metallocene-catalyzed polymers, single-site catalyst polymerized polymers, high crystalline acid polymers, cationic ionomers, and combinations thereof. Particular polyolefins suitable for blending include one or more, linear, branched, or cyclic, C₂–C₄₀ olefins, particularly polymers comprising ethylene or propylene copolymerized with one or more C₂–C₄₀ olefins, C₃–C₂₀ α-olefins, or C₃–C₁₀ α-olefins. Particular conventional HNPs suitable for blending include, but are not limited to, one or more of the HNPs disclosed in U.S. Pat. Nos. 6,756,436, 6,894,098, and 6,953,820, the entire disclosures of which are hereby incorporated herein by reference. Examples of elastomers suitable for blending with the invention polymers include natural and synthetic rubbers, including, but not limited to, ethylene propylene rubber (“EPR”), ethylene propylene diene rubber (“EPDM”), styrenic block copolymer rubbers (such as SI, SIS, SB, SBS, SIBS, and the like, where “S” is styrene, “I” is isobutylene, and “B” is butadiene), butyl rubber, halobutyl rubber, copolymers of isobutylene and para-alkylstyrene, halogenated copolymers of isobutylene and para-alkylstyrene, natural rubber, polyisoprene, copolymers of butadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, and polybutadiene rubber (cis and trans). Additional suitable blend polymers include those described in U.S. Pat. No. 5,981,658, for example at column 14, lines 30 to 56, the entire disclosure of which is hereby incorporated herein by reference. The blends described herein may be produced by post-reactor blending, by connecting reactors in series to make reactor blends, or by using more than one catalyst in the same reactor to produce multiple species of polymer. The polymers may be mixed prior to being put into an extruder, or they may be mixed in an extruder.

Particularly suitable low modulus HNP compositions include, but are not limited to, the highly-resilient thermoplastic compositions disclosed in U.S. Patent Application Publication No. 2005/0148725; the highly-neutralized ethylene copolymers disclosed in U.S. Pat. Nos. 6,653,382 and 6,777,472, and U.S. Patent Application Publication No. 2003/0130434; and the highly-resilient thermoplastic elastomer compositions disclosed in U.S. Pat. No. 6,815,480; the entire disclosures of which are hereby incorporated herein by reference.

High Modulus HNP Composition

High modulus HNP compositions of the present invention comprise at least one high modulus HNP having a modulus within the range having a lower limit of 25,000 or 27,000 or 30,000 or 40,000 or 45,000 or 50,000 or 55,000 or 60,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi.

High modulus HNPs of the present invention are salts of acid copolymers. It is understood that the high modulus HNP may be a blend of two or more high modulus HNPs. Preferred acid copolymers are copolymers of an α-olefin and a C₃–C₈ α,β-ethylenically unsaturated carboxylic acid. The acid is typically present in the acid copolymer in an amount within the range having a lower limit of 1 or 10 or 12 or 15 or 20 wt % and an upper limit of 25 or 30 or 35 or 40 wt %, based on the total weight of the acid copolymer. The α-olefin is preferably selected from ethylene and propylene. The acid is preferably selected from (meth) acrylic acid, ethacrylic acid, maleic acid, crotonic acid, fumaric acid, and itaconic acid. (Meth) acrylic acid is particularly preferred. In a preferred embodiment, the high modulus HNP has a higher level of acid than the low modulus HNP.

Suitable acid copolymers include partially neutralized acid polymers. Examples of suitable partially neutralized acid polymers include, but are not limited to, Surlyn® ionomers, commercially available from E.I. du Pont de Nemours and Company; AClyn® ionomers, commercially available from Honeywell International Inc.; and Iotek® ionomers, commercially available from ExxonMobil Chemical Company. Also suitable are DuPont® HPF 1000 and DuPont® HPF 2000, ionomeric materials commercially available from E.I. du Pont de Nemours and Company. Additional suitable acid polymers are more fully described, for example, in U.S. Pat. Nos. 6,562,906, 6,762,246, and 6,953,820 and U.S. Patent Application Publication Nos. 2005/0049367, 2005/0020741, and 2004/0220343, the entire disclosures of which are hereby incorporated herein by reference.

In a preferred embodiment, the high modulus HNP is formed by reacting an acid copolymer with a sufficient amount of cation source such that at least 80%, preferably at least; 90%, more preferably at least 95%, and even more preferably 100%, of all acid groups present are neutralized. Suitable cation sources include metal ions and compounds of alkali metals, alkaline earth metals, and transition metals; metal ions and compounds of rare earth elements; silicone, silane, and silicate derivatives and complex ligands; and combinations thereof. Preferred cation sources are metal ions and compounds of magnesium, sodium, potassium, cesium, calcium, barium, manganese, copper, zinc, tin, lithium, and rare earth metals. Metal ions and compounds of calcium and magnesium are particularly preferred. The acid copolymer may be at least partially neutralized prior to contacting the acid copolymer with the cation source to form the high modulus HNP. As previously stated, methods of preparing ionomers, and the acid copolymers on which ionomers are based, are disclosed, for example, in U.S. Pat. Nos. 3,264,272, and 4,351,931, and U.S. Patent Application Publication No. 2002/0013413.

High modulus HNP compositions of the present invention optionally contain one or more melt flow modifiers. The amount of melt flow modifier in the composition is readily determined such that the melt flow index of the composition is at least 0.1 g/10 min, preferably from 0.5 g/10 min to 10.0 g/10 min, and more preferably from 1.0 g/10 min to 6.0 g/10 min, as measured using ASTM D-1238, condition E, at 190° C., using a 2160 gram weight.

Suitable melt flow modifiers include, but are not limited to, high molecular weight organic acids and salts thereof, polyamides, polyesters, polyacrylates, polyurethanes, polyethers, polyureas, polyhydric alcohols, and combinations thereof. Suitable organic acids are aliphatic organic acids, aromatic organic acids, saturated mono-functional organic acids, unsaturated monofunctional organic acids, multi-unsaturated mono-functional organic acids, and dimerized derivatives thereof. Particular examples of suitable organic acids include, but are not limited to, caproic acid, caprylic acid, capric acid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylacetic acid, naphthalenoic acid, dimerized derivatives thereof. Suitable organic acids are more fully described, for example, in U.S. Pat. No. 6,756,436, the entire disclosure of which is hereby incorporated herein by reference.

Additional melt flow modifiers suitable for use in compositions of the present invention, include the non-fatty acid melt flow modifiers described in copending U.S. patent application Ser. Nos. 11/216,725 and 11/216,726, the entire disclosures of which are hereby incorporated herein by reference.

High modulus HNP compositions of the present invention optionally include additive(s) and/or filler(s) in an amount within the range having a lower limit of 0 or 5 or 10 wt %, and an upper limit of 25 or 30 or 50 wt %, based on the total weight of the high modulus HNP composition. Suitable additives and fillers include those previously described as suitable for the low modulus HNP compositions of the present invention.

In addition to the high modulus HNP, optional melt flow modifier(s), and optional additive(s) and/or filler(s), the high modulus HNP composition of the present invention may contain a low modulus HNP.

In a particular embodiment, the high modulus HNP composition has an MVTR of 8 g-mil/100 in²/day or less (i.e., 3.2 g-mm/m²·day or less), or 5 g-mil/100 in²/day or less (i.e., 2.0 2·day or less), or 3 g-mil/100 in²/day or less (i.e., 1.2 g-mm/m²·day or less), or 2 g-mil/100 in²/day or less (i.e., 0.8 g-mm/m²·day or less), or 1 g-mil/100 in²/day or less (i.e., 0.4 2·day or less), or less than 1 g-mil/100 in²/day (i.e., less than 0.4 g-mm/m²·day). In a preferred aspect of this embodiment, the high modulus HNP composition comprises a high modulus HNP prepared using a cation source which is less hydrophilic than conventional magnesium-based cation sources. Suitable moisture resistant HNP compositions are disclosed, for example, in copending U.S. patent application Ser. No. 11/270,066 and U.S. Patent Application Publication No. 2005/0267240, the entire disclosures of which are hereby incorporated herein by reference.

High modulus HNP compositions of the present invention are not limited by any particular method or any particular equipment for making the compositions. In a preferred embodiment, the composition is prepared by the following process. The acid polymer(s), preferably an ethylene/(meth) acrylic acid copolymer, optional melt flow modifier(s), and optional additive(s)/filler(s) are simultaneously or individually fed into a melt extruder, such as a single or twin screw extruder. A suitable amount of cation source is then added such that at least 80%, preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of all acid groups present are neutralized. The acid polymer may be at least partially neutralized prior to the above process. The components are intensively mixed prior to being extruded as a strand from the die-head.

In another preferred embodiment, the high modulus HNP composition is formed by combining a low modulus HNP with a sufficient amount of one or more additional material(s), including, but not limited to, additives, fillers, and polymeric materials, to increase the modulus such that the resulting composition has a modulus as described above for the high modulus HNP.

HNP compositions of the present invention may be blended with one or more additional polymers, such as thermoplastic polymers and elastomers. Examples of thermoplastic polymers and elastomers suitable for blending include those previously described as suitable for blending with the low modulus HNP compositions of the present invention.

Golf Ball Applications

Golf balls of the present invention comprise at least one layer formed from a low modulus HNP composition and at least one layer formed from a high modulus HNP composition. In a preferred embodiment, the present invention provides a golf ball having a dual core and a cover, wherein the dual core includes a layer formed from a low modulus HNP composition and a layer formed from a high modulus HNP composition. The cover may be a single layer or dual cover.

Suitable cover layer materials for the golf balls disclosed herein include, but are not limited to, ionomer resin and blends thereof (particularly Surlyn® ionomer resin), polyurethanes, polyureas, (meth)acrylic acid, thermoplastic rubber polymers, polyethylene, and synthetic or natural vulcanized rubber, such as balata. When used as cover layer materials, polyurethane and polyurea can be thermoset or thermoplastic. Thermoset materials can be formed into golf ball layers by conventional casting or reaction injection molding techniques. Thermoplastic materials can be formed into golf ball layers by conventional compression or injection molding techniques. Light stable polyureas and polyurethanes are preferred for the outer cover layer material. Additional suitable cover and rubber core materials are disclosed, for example, in U.S. Patent Application Publication No. 2005/0164810, U.S. Pat. No. 5,919,100, and PCT Publications WO00/23519 and WO00/29129, the entire disclosures of which are hereby incorporated herein by reference. In embodiments of the present invention wherein a golf ball having a single layer cover is provided, the cover layer material is preferably selected from polyurethane and polyurea. In embodiments of the present invention wherein a golf ball having a dual cover is provided, the inner cover layer is preferably a high modulus thermoplastic, and the outer cover layer is preferably selected from polyurethane and polyurea.

The present invention is not limited by any particular process for forming the golf ball layer(s). It should be understood that the layer(s) can be formed by any suitable technique, including injection molding, compression molding, casting, and reaction injection molding.

In the embodiments disclosed herein, the low modulus HNP composition and/or the high modulus HNP composition, can be either foamed or filled with density adjusting materials to provide desirable golf ball performance characteristics.

Golf ball cores of the present invention, including dual cores and multi-layered cores, typically have an Atti compression of less than 100, and preferably have an Atti compression within the range having a lower limit of 20 or 50 and an upper limit of 80 or 90 or 100. Golf ball cores of the present invention typically have a coefficient of restitution (“COR”) at 125 ft/s of at least 0.75, preferably at least 0.78, and more preferably at least 0.79. As used herein, COR is defined as the ratio of the rebound velocity to the inbound velocity when balls are fired into a rigid plate. In determining COR, the inbound velocity is understood to be 125 ft/s.

Golf balls of the present invention typically have an Atti compression of less than 120, and preferably have an Atti compression within the range having a lower limit of 60 or 75 and an upper limit of 105 or 110 or 120. Golf balls of the present invention typically have a coefficient of restitution (“COR”) at 125 ft/s of at least 0.75, preferably at least 0.78, and more preferably at least 0.79.

Dual Core/Single Cover Golf Balls

In one embodiment, the present invention provides a golf ball comprising an inner core layer formed from a low modulus HNP composition, an outer core layer formed from a high modulus HNP composition, and a cover having a single layer. In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of 80 or less, or 70 or less, or 65 or less. In yet another particular aspect of this embodiment, the low modulus HNP of the inner core layer composition has a modulus within the range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 17,000 or 28,000 or 30,000 or 50,000 psi and the high modulus HNP of the outer core layer composition has a modulus within the range having a lower limit of 45,000 or 55,000 or 60,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi.

In another embodiment, the present invention provides a golf ball comprising an inner core layer formed from a high modulus HNP composition, an outer core layer formed from a low modulus HNP composition, and a cover having a single layer. In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of at least 80, and preferably has an Atti compression within the range having a lower limit of 80 or 90 or 100 and an upper limit of 130 or 140. In yet another particular aspect of this embodiment, the high modulus HNP of the inner core layer composition has a modulus within the range having a lower limit of 25,000 or 27,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi and the low modulus HNP of the outer core layer composition has a modulus within the range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 28,000 or 30,000 or 50,000 psi.

Dual Core/Dual Cover Golf Balls

In another embodiment, the present invention provides a golf ball comprising an inner core layer formed from a low modulus HNP composition, an outer core layer formed from a high modulus HNP composition, and a dual cover. In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the dual cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.060 inches and an upper limit of 0.075 or 0.090 or 0.110 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of 80 or less, or 70 or less, or 65 or less. In yet another particular aspect of this embodiment, the low modulus HNP of the inner core layer composition has a modulus within the range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 17,000 or 28,000 or 30,000 or 50,000 psi and the high modulus HNP of the outer core layer composition has a modulus within the range having a lower limit of 45,000 or 55,000 or 60,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi.

In another embodiment, the present invention provides a golf ball comprising an inner core layer formed from a high modulus HNP composition, an outer core layer formed from a low modulus HNP composition, and a dual cover. In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the dual cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.060 inches and an upper limit of 0.075 or 0.090 or 0.110 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of at least 80, and preferably has an Atti compression within the range having a lower limit of 80 or 90 or 100 and an upper limit of 130 or 140. In yet another particular aspect of this embodiment, the high modulus HNP of the inner core layer composition has a modulus within the range having a lower limit of 25,000 or 27,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi and the low modulus HNP of the outer core layer composition has a modulus within the range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 28,000 or 30,000 or 50,000 psi.

Golf Balls Having Multi-Layered Cores

By the present invention, it has been found that, in some embodiments, the use of a low modulus HNP-based layer and a high modulus HNP-based layer eliminates the need for conventional rubber-based layers. However, it is contemplated that it may be desirable to include conventional rubber-based layers in some embodiments of the present invention.

Thus, in one embodiment, the present invention provides a golf ball comprising:

-   -   (a) an inner core layer comprising a rubber composition,     -   (b) an intermediate core layer formed from a low modulus HNP         composition,     -   (c) an outer core layer formed from a high modulus HNP         composition, and     -   (d) a cover having one or more layers.

In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the intermediate core layer has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.150 or 0.220 or 0.280 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of 80 or less, or 70 or less, or 65 or less. In yet another particular aspect of this embodiment, the low modulus HNP of the intermediate core layer composition has a modulus within the range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 17,000 or 28,000 or 30,000 or 50,000 psi and the high modulus HNP of the outer core layer composition has a modulus within the range having a lower limit of 45,000 or 55,000 or 60,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi.

In another embodiment, the present invention provides a golf ball comprising:

-   -   (a) an inner core layer formed from a low modulus HNP         composition,     -   (b) an intermediate core layer comprising a rubber composition,     -   (c) an outer core layer formed from a high modulus HNP         composition, and     -   (d) a cover having one or more layers.

In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the intermediate core layer has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.150 or 0.220 or 0.280 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of 80 or less, or 70 or less, or 65 or less.

In another embodiment, the present invention provides a golf ball comprising:

-   -   (a) an inner core layer formed from a low modulus HNP         composition,     -   (b) an intermediate core layer formed from a high modulus HNP         composition,     -   (c) an outer core layer comprising a rubber composition, and     -   (d) a cover having one or more layers.

In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the intermediate core layer has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.150 or 0.220 or 0.280 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of 80 or less, or 70 or less, or 65 or less.

In another embodiment, the present invention provides a golf ball comprising:

-   -   (a) an inner core layer comprising a rubber composition,     -   (b) an intermediate core layer formed from a high modulus HNP         composition,     -   (c) an outer core layer formed from a low modulus HNP         composition, and     -   (d) a cover having one or more layers.

In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the intermediate core layer has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.150 or 0.220 or 0.280 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of 80 or less, or 70 or less, or 65 or less. In yet another particular aspect of this embodiment, the high modulus HNP of the intermediate core layer composition has a modulus within the range having a lower limit of 25,000 or 27,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi and the low modulus HNP of the outer core layer composition has a modulus within the range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 28,000 or 30,000 or 50,000 psi.

In another embodiment, the present invention provides a golf ball comprising:

-   -   (a) an inner core layer formed from a high modulus HNP         composition,     -   (b) an intermediate core layer formed from a low modulus HNP         composition,     -   (c) an outer core layer comprising a rubber composition, and     -   (d) a cover having one or more layers.

In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the intermediate core layer has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.150 or 0.220 or 0.280 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of at least 80, and preferably has an Atti compression within the range having a lower limit of 80 or 90 or 100 and an upper limit of 130 or 140.

In another embodiment, the present invention provides a golf ball comprising:

-   -   (a) an inner core layer formed from a high modulus HNP         composition,     -   (b) an intermediate core layer comprising a rubber composition,     -   (c) an outer core layer formed from a low modulus HNP         composition, and     -   (d) a cover having one or more layers.

In a particular aspect of this embodiment, the inner core layer has a diameter within the range having a lower limit of 0.500 or 0.750 or 1.000 inches and an upper limit of 1.550 or 1.570 or 1.580 inches; the intermediate core layer has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.150 or 0.220 or 0.280 inches; the outer core has a thickness within the range having a lower limit of 0.020 or 0.025 or 0.032 inches and an upper limit of 0.310 or 0.440 or 0.560 inches; and the cover has an overall thickness within the range having a lower limit of 0.020 or 0.025 or 0.030 inches and an upper limit of 0.065 or 0.080 or 0.090 inches. In another particular aspect of this embodiment, the inner core layer has an Atti compression of at least 80, and preferably has an Atti compression within the range having a lower limit of 80 or 90 or 100 and an upper limit of 130 or 140.

Suitable rubbers for golf ball layers of the present invention include natural and synthetic rubbers, including, but not limited to, polybutadiene, polyisoprene, ethylene propylene rubber (“EPR”), ethylene propylene diene rubber (“EPDM”), styrenic block copolymer rubbers (such as SI, SIS, SB, SBS, SIBS, and the like, where “S” is styrene, “I” is isobutylene, and “B” is butadiene), butyl rubber, halobutyl rubber, copolymers of isobutylene and para-alkylstyrene, halogenated copolymers of isobutylene and para-alkylstyrene, copolymers of butadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, and combinations thereof. Diene rubbers are preferred.

In embodiments wherein the inner core layer comprises a rubber composition, the inner core layer is preferably formed from a reaction product of a rubber, a crosslinking agent, a filler, a co-crosslinking agent or free radical initiator, and optionally a cis-to-trans catalyst. The rubber is preferably selected from polybutadiene and styrene-butadiene. The crosslinking agent typically includes a metal salt, such as a zinc salt or magnesium salt, of an acid having from 3 to 8 carbon atoms, such as (meth) acrylic acid. The free radical initiator can be any known polymerization initiator which decomposes during the cure cycle, including, but not limited to, dicumyl peroxide, 1,1-di-(t-butylperoxy) 3,3,5-trimethyl cyclohexane, a-a bis-(t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5 di-(t-butylperoxy) hexane or di-t-butyl peroxide, and mixtures thereof. Suitable types and amounts of rubber, crosslinking agent, filler, co-crosslinking agent, and initiator are more fully described in, for example, U.S. Patent Application Publication No. 2003/0144087, the entire disclosure of which is hereby incorporated herein by reference. Reference is also made to U.S. Patent Application Publication No. 2003/0144087 for various ball constructions and materials that can be used in golf ball core, intermediate, and cover layers.

Wound Golf Balls

In one embodiment, the present invention provides a wound golf ball comprising a core, a conventional elastomeric winding wound around the core, and a cover made from a conventional golf ball cover material, e.g., ionomer resin and blends thereof (particularly Surlyn® ionomer resin), thermoset polyurethanes and polyureas, thermoplastic polyurethanes and polyureas, (meth)acrylic acid, thermoplastic rubber polymers, polyethylene, and synthetic or natural vulcanized rubber, such as balata.

In a particular aspect of this embodiment, the core includes an inner core layer formed from a low modulus HNP composition and an outer core layer formed from a high modulus HNP composition. The inner core layer preferably has a diameter of from 0.500 to 1.250 inches. The outer core layer preferably has a thickness of from 0.125 to 0.525 inches. The overall core diameter is preferably from 1.000 to 1.550 inches.

In another particular aspect of this embodiment, the core includes an inner core layer formed from a high modulus HNP composition and an outer core layer formed from a low modulus HNP composition. The inner core layer preferably has a diameter of from 0.500 to 1.250 inches. The outer core layer preferably has a thickness of from 0.125 to 0.525 inches. The overall core diameter is preferably from 1.000 to 1.550 inches.

Wound golf balls of the present invention are manufactured by well known techniques, such as those disclosed, for example, in U.S. Pat. No. 4,846,910.

Additional Examples of Suitable HNPs

The HNPs of the table below have been found to be particularly useful as the low modulus HNP and/or the high modulus HNP of the present invention.

Flexural Hardness**, Hardness**, cation Modulus*, Shore C Shore D Example source psi (18 day) (annealed) 1 Ca/Mg 71,600 88 57 2 Ca/Li 70,300 89 58 3 Ca 70,100 92 60 4 Ca/Zn 60,400 88 58 5 Mg 38,300 84 52 6 Mg 27,600 84 52 7 Mg 16,300 78 45 8 Mg 10,600 70 40 9 Mg 10,400 69 39 *Flexural modulus was measured according to ASTM D790-03 Procedure B. **Hardness was measured according to ASTM D2240.

In embodiments of the present invention directed to a golf ball having an inner core layer or intermediate core layer formed from a low modulus HNP composition, Examples 6–9 are particularly suitable for use as the low modulus HNP composition of the inner core layer or intermediate core layer.

In embodiments of the present invention directed to a golf ball having an outer core layer formed from a low modulus HNP composition, Examples 5–9 are particularly suitable for use as the low modulus HNP composition of the outer core layer.

In embodiments of the present invention directed to a golf ball having an inner core layer or intermediate core layer formed from a high modulus HNP composition, Examples 1–6 are particularly suitable for use as the high modulus HNP composition of the inner core layer or intermediate core layer.

In embodiments of the present invention directed to a golf ball having an outer core layer formed from a high modulus HNP composition, Examples 1–4 are particularly suitable for use as the high modulus HNP composition of the outer core layer.

When numerical lower limits and numerical upper limits are set forth herein, it is contemplated that any combination of these values may be used.

All patents, publications, test procedures, and other references cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for all jurisdictions in which such incorporation is permitted.

While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those of ordinary skill in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein, but rather that the claims be construed as encompassing all of the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those of ordinary skill in the art to which the invention pertains. 

1. A golf ball comprising: (a) an inner core layer formed from a low modulus HNP composition, the low modulus HNP composition comprising: a highly neutralized ethylene/(meth) acrylic acid/alkyl (meth) acrylate copolymer having a modulus of from 1,000 psi to 50,000 psi; (b) an outer core layer formed from a high modulus HNP composition, the high modulus HNP composition comprising: a highly neutralized ethylene/(meth)acrylic acid copolymer having a modulus of from 45,000 psi to 150,000 psi; and (c) a cover; wherein the modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 10% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.
 2. The golf ball of claim 1, wherein the modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 25% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.
 3. The golf ball of claim 1, wherein the highly neutralized copolymer of the low modulus HNP composition has a modulus of from 1,000 psi to 35,000 psi.
 4. The golf ball of claim 3, wherein the modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 25% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.
 5. The golf ball of claim 1, wherein one or both of the inner core layer and outer core layer is foamed.
 6. The golf ball of claim 1, wherein the low modulus HNP composition has a modulus of from 1,000 psi to 50,000 psi, and wherein the high modulus HNP composition has a modulus of from 45,000 psi to 150,000 psi.
 7. The golf ball of claim 6, wherein the modulus of the low modulus HNP composition is at least 25% less than the modulus of the high modulus HNP composition.
 8. The golf ball of claim 1, wherein the high modulus HNP composition has a moisture vapor transmission rate of 8 g-mil/100 in²/day or less (3.2 g-mm/m²·day or less).
 9. The golf ball of claim 1, wherein the cover is a single layer having a thickness of from 0.020 inches to 0.090 inches and is formed from a thermoplastic or thermoset material.
 10. The golf ball of claim 1, wherein the cover comprises two or more layers and has an overall thickness of from 0.020 inches to 0.110 inches, and wherein each cover layer is formed from a thermoplastic or thermoset material.
 11. The golf ball of claim 1, wherein the golf ball additionally comprises an intermediate core layer disposed between the inner core layer and the outer core layer, wherein the intermediate core layer is formed from a diene rubber composition.
 12. A golf ball comprising: (a) an inner core layer formed from a high modulus HNP composition, the high modulus HNP composition comprising: a highly neutralized ethylene/(meth)acrylic acid copolymer having a modulus of from 25,000 psi to 150,000 psi; (b) an outer core layer formed from a low modulus HNP composition, the low modulus HNP composition comprising: a highly neutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer having a modulus of from 1,000 psi to 50,000 psi; and (c) a cover; wherein the modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 10% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.
 13. The golf ball of claim 12, wherein one or both of the inner core layer and outer core layer is foamed.
 14. The golf ball of claim 12, wherein the modulus of the highly neutralized copolymer of the low modulus HNP composition is at least 25% less than the modulus of the highly neutralized copolymer of the high modulus HNP composition.
 15. The golf ball of claim 12, wherein the high modulus HNP composition has a modulus of from 25,000 psi to 150,000 psi, and wherein the low modulus HNP composition has a modulus of from 1,000 psi to 50,000 psi.
 16. The golf ball of claim 12, wherein the high modulus HNP composition has a modulus of from 25,000 psi to 75,000 psi, and wherein the low modulus HNP composition has a modulus of from 1,000 psi to 50,000 psi.
 17. The golf ball of claim 16, wherein the modulus of the low modulus HNP composition is at least 25% less than the modulus of the high modulus HNP composition.
 18. The golf ball of claim 12, wherein the low modulus HNP composition has a moisture vapor transmission rate of 8 g-mil/100 in²/day or less (3.2 g-mm/m²·day or less).
 19. The golf ball of claim 12, wherein the cover is a single layer having a thickness of from 0.020 inches to 0.090 inches and is formed from a thermoplastic or thermoset material.
 20. The golf ball of claim 12, wherein the cover comprises two or more layers and has an overall thickness of from 0.020 inches to 0.110 inches, and wherein each cover layer is formed from a thermoplastic or thermoset material. 